The present invention is concerned with a vehicle wheel antiskid brake control system of the type in which a reference velocity signal approximating the vehicle speed is generated for comparison with an individual wheel speed signal to obtain a velocity signal .DELTA.V when a predetermined difference exists therebetween. The velocity signal .DELTA.V is used in the antiskid system to control the reapplication of brake pressure at the individual wheel following a skid thereof. The reference velocity signal V.sub.REF, represented in the velocity curve of FIG. 1, is formed in accordance with a speed voltage arising from at least one wheel of the vehicle when the wheel is accelerating at a speed V.sub.R above the reference velocity signal and when decelerating at a rate below a preselected skid threshold. When the deceleration rate exceeds the skid threshold, a special memory circuit functions such that only a gradual decay of the reference voltage signal V.sub.REF occurs from a value corresponding to the wheel speed V.sub.R at the time the wheel deceleration exceeds the skid threshold. Normally, this would result in only a slight deviation between the reference velocity signal V.sub.REF approximating the vehicle velocity and the actual vehicle velocity signal V.sub.F before the velocity signal .DELTA.V disappears to establish the reapplication of brake pressure. The inertia of the reaccelerating wheel will thus allow the wheel speed to approach the vehicle speed before another cycle of wheel skid control is initiated so that the reference velocity signal V.sub.REF remains a fairly true approximation of the actual vehicle velocity V.sub.F throughout the wheel skid brake control cycle.
On roadways having a low coefficient of friction, however, such as experienced by a vehicle traveling on an ice covered road, the reacceleration of a wheel following a wheel skid is, of course, relatively slow so that by the time the velocity signal .DELTA.V disappears to establish the reapplication of brake pressure, the wheel speed is still relatively low. Accordingly, another cycle of wheel skid control will be initiated before the wheel speed V.sub.R is restored to a level sufficient to reestablish the reference velocity signal V.sub.REF as an accurate approximation of the vehicle velocity V.sub.F. It will be appreciated, therefore, that following several cycles of wheel skid control operation, a considerable deviation between the actual vehicle velocity V.sub.F and reference velocity signal V.sub.REF will have been accumulated such that the wheel speed V.sub.R will eventually become zero, while the vehicle is still moving. Since the reference velocity signal V.sub.REF is generated as a function of the wheel speed, it also will now be essentially zero so that the non-rotating state of the wheel will be undetected and the wheel will remain locked in a skid condition in spite of the antiskid brake control system.